> The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 V/mV.
> Which I think is a bit low, but then, the opamp is old.
Check other datasheets, that's definitely wrong
David
___
volt-nuts mailing list -- volt-nuts@febo.com
To

1) Reverse the supplies on U4 (in real circuit reversed supplies will fry the
chip.)
2) Add 10k in series with reset switch
3) Swap connections to U4 inputs.
4) Use series shunt switch for reset switch as used in an actual 3458A.
Once done together with swapping in LT1220 for LT1225 rest works as

Attila
Some insight can be gleaned by using a single pole model for an opamp
configured as an integrator and deriving the expression for the output signal.
Look at the non linearity in the output.
Look at the voltage at the inverting input.
The effective impedance at the inverting input due to

Why do you think that the datasheet is wrong?
Its the same as the 1989 version.
A lot of the early wideband opamps didn't have high open loop gain.
Even the LT1220 only has about 7 - 15x more gain at rated load.
The LT1220 has a a pair of cascaded complementary symmetry emitter followers in

On Fri, 23 Feb 2018 18:48:24 -
"David C. Partridge" wrote:
> Looking your schematic, I see that you are using LT1225 for both U2 (U111)
> and U3 (U112)
>
> Why did you use those rather than LM6361 and AD848? Was it just because
> LTSpice didn't have models

The April 1989 HP Journal is mostly dedicated to the 3458A and there's an
article about the dual slope integrator starting on page 8.
There's also a nice discussion about it in Art of Electronics 3rd Edition
starting on page 918
HtH
David
-Original Message-
From: volt-nuts

On Fri, 23 Feb 2018 17:14:28 -
"David C. Partridge" wrote:
> The April 1989 HP Journal is mostly dedicated to the 3458A and there's an
> article about the dual slope integrator starting on page 8.
>
> There's also a nice discussion about it in Art of

On Fri, 23 Feb 2018 18:31:47 +0100
Attila Kinali wrote:
> And why are U2 and U3 wired up the way they are?
Let me expand here a little bit to make it clear what puzzles me.
The HP3458 circuit uses 3 opamps: LT1001, LM6361 and AD848.
The LT1001 is there for its low input bias

Moin,
I am trying to understand how the HP 3458 integrator of its
dual-slope ADC works, as it's a bit more complicated than
a simple, single opamp integrator. As you can see from the
attached picture, it consists of 3 opamps (U1-U3) for the
integrator itself, and another for the slope

Looking your schematic, I see that you are using LT1225 for both U2 (U111) and
U3 (U112)
Why did you use those rather than LM6361 and AD848? Was it just because
LTSpice didn't have models for them? It can make a difference ...
As for why they chose to use 3 op-amps rather than 2? I don't

Moin attila
I'd start with simulating and understanding the integrator in the 34401A, its a
little simpler but still has a coupe of opamps in the integrator. Then
analysing the GBW requirements of the various opamps used in the HP3458A shoul
become somewhat clearer.
Bruce
>
> On 24

Hint: start by looking at the summing junction voltage of a single opamp
integrator with R = 50k, C = 330pF.
NB the LT1225 isnt unity gain stable so its use for any of U2, U3 and U4 is
questionable.
They will all likely oscillate on their own.
Bruce
>
> On 24 February 2018 at 08:45

Good evening!
On Fri, 23 Feb 2018 19:02:42 -
"David C. Partridge" wrote:
> This is a bit time delayed as the attachment was too large, but posting
> anyway
Ah.. I have the HP3458 schematics, that's where my circuit comes from.
Maybe I should have made that